Antioxidant and tyrosinase inhibition properties of leaves and rhizomes of ginger species

Total phenolic content (TPC) and ascorbic acid equivalent antioxidant capacity (AEAC) of leaves of 26 ginger species belonging to nine genera and three tribes were screened. For 14 species, TPC and AEAC of rhizomes were also assessed. Ferrous ion-chelating (FIC) abilities of leaves and rhizomes of eight species were compared. Leaves of five species of Etlingera were analysed for tyrosinase inhibition activity. Of the 26 species, leaves of Etlingera species had the highest TPC and AEAC. Eleven of the 14 species had significantly higher TPC and/or AEAC in leaves than in rhizomes. Values of leaves of Etlingera elatior and Etlingera maingayi were seven to eight times higher than those of rhizomes. In terms of FIC ability, six of the eight species clearly showed higher values in leaves than in rhizomes. The most outstanding was the FIC value of Alpinia galanga leaves which was more than 20 times higher than that of rhizomes. Of the five species of Etlingera, leaves of E. elatior displayed the strongest tyrosinase inhibition activity, followed by leaves of Etlingera fulgens and E. maingayi. Values of their inhibition activity were significantly higher than or comparable to the positive control. Besides promising tyrosinase inhibition ability, leaves of these three Etlingera species also have high antioxidant activity and antibacterial properties.